Unusual use of ssh

[Derek Ragona]

At 06:35 PM 5/21/2008, Doug Hardie wrote:
>I have an unusual situation that I suspect is not practical, but just
>in case...
>
>I have a class C network with a T1 to the internet.  There are a
>number of hosts on that network.  Unfortunately the T1 line is just
>part of a path with several additional links before it gets to the
>upstream ISP.  Some of those links are relatively prone to outages.
>In the same facility, I have a number of WiFi access points that are
>connected through a router to a DSL connection to the internet.  That
>path is completely independent from the T1 and actually goes through a
>completely different set of central offices.
>
>What I have tried to do is to link the DSL router to one of my hosts
>via a separate NIC and address that is on the LAN of the WiFi router.
>So far all is good.  I can ping any of the access points from that
>host just fine.  I have established a pass through port in the DSL
>router for SSH that sends the packets to that host.  Sure enough, ssh
>packets are received by the host.  The problem is that it does not
>respond on the right interface.  The routing table uses a default
>route through the T1.  Thats where the sshd responses are being sent.
>
>Since I have no a priori knowledge what IPs I would have available
>when I need to use this back door, I can't pre-setup the routing
>table.  I need sshd to respond on the same interface it receives the
>packets from.  I don't believe that is possible using IPv4 routing.  I
>think that it is using IPv6 but none of the networks involved support
>that yet.  I don't find any option in sshd to force it to respond on
>the right interface either.  Is there something I have missed?

You need to set the correct listen address in /etc/sshd_config then restart 
sshd.

Also you may need to provide a route for this interface if it cannot find 
it's own route.

         -Derek

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